Most air conditioning systems operate under the Rankine cycle. These systems usually have an electrically driven compressor that increases the pressure and temperature of a refrigerant. While in this condition, the refrigerant is passed through a radiator, or the like, which allows heat exchange with ambient temperatures. This lowers the refrigerant temperature while maintaining an elevated pressure. Afterward, the refrigerant is depressurized by expansion through an orifice. This causes its temperature to be cooled to well below ambient. The cold refrigerant is then used in a heat exchanger to produce a cool or cold supply of air. As a result, the temperature of the refrigerant increases in the heat exchanger. It is cooled once again by compression and heat exchange in a repeat of the sequence just described.
Desiccant cooling systems have been used as an alternative to Rankine cycle and other kinds of air conditioning systems. Desiccant cooling involves the use of an adsorption/desorption cycle. They are known as Pennington cycle systems when all the air supplied to the conditioned space comes from the ambient. Some systems recirculate air from the conditioned space or, perhaps, use a combination of ambient and recirculated air.
In the typical desiccant system, a fresh supply of ambient air is brought into contact with a desiccant material. The desiccant decreases the humidity, and, at the same time, the energy released during adsorption ("heat of adsorption") causes the temperature of the air to increase. The air temperature is then reduced--first by a sensible heat exchanger and then by an adiabatic humidifier. After leaving the humidifier, the supply is relatively dry and cooler than its original ambient temperature.
There are many variations of Rankine and desiccant type systems which utilize the basic modes of cooling generally described above for each system. Rankine systems have the capability of providing a greater range of cooling than desiccant systems, but at a greater energy cost. However, there is a disadvantage associated with Rankine systems in that they commonly use chlorofluorocarbons or other undesireable chemicals as refrigerants, some of which are toxic.
Chlorofluorocarbons have been identified as chemical agents which are potentially harmful to the environment. Notably, they have been linked to ozone depletion of the atmosphere. Other refrigerants such as ammonia or sulfur dioxide are toxic and can be hazardous or flammable if released from the system.
Desiccant systems provide a more environmentally benign way of providing air conditioning. Not only can they be used to cool air, but they can also remove certain environmental contaminants in the air as it is supplied to a room or other conditioned space.
A common operational characteristic of desiccant systems is that the desiccant eventually becomes saturated with moisture and must be regenerated in some fashion. In the known prior art, this has usually been done by mounting the desiccant on a wheel that rotates continually.
A portion of the wheel is in the path of the supply air which is being cooled and exhausted to a room or space requiring conditioned air. Another portion of the wheel is in the path of a heated airstream. As the wheel rotates, individual wheel section areas are alternately impacted by the supply air, from which moisture is adsorbed, and then by the heated air which regenerates the desiccant. This type of system has several major limitations.
First, a wheel apparatus can only carry a fixed amount of desiccant. This fixes the conditions of moisture adsorption and desorption by regeneration in a relatively inflexible manner. Second, the wheel must be relatively large because of the structural matrix required to support the desiccant material. Usually, some kind of honeycomb arrangement is utilized to hold the desiccant in place as the wheel rotates. Third, driving the wheel in rotation requires energy which detracts from the system's overall operating efficiency. Last, the manufacturing and maintenance costs associated with the wheel drives up system costs. Part of the maintenance problem associated with a wheel is that, over time, the desiccant may degrade or be lost from the system necessitating replacement. It is difficult to replace the desiccant alone in a wheel structure without replacing the entire wheel.
The purpose of the present invention is to provide a desiccant cooling system that eliminates the disadvantages of the rotating wheel system described above.